The invention relates to methods and apparatus for the manufacture of cement from raw cement meal and particularly wherein the process includes preheating with a series of cyclones, calcining in a calcining and sintering in a rotary furnace and thereafter cooling.
In German published application No. 33 33 705, there is disclosed a method and apparatus for the manufacture of cement clinker low in harmful substances, particularly in alkali. In the structure disclosed therein, the preheated raw meal is divided into two substreams where one substream is introduced into the exhaust gas stream from the rotary tubular kiln and the other substream is introduced into the exhaust air stream of the clinker cooler and the substreams are calcined. The calcined substreams are thereafter introduced into the lowest cyclone separator and combined to form a single suspension gas stream and thereafter are separated from the exhaust gases in the last cyclone separator. In this manner, the performance capability of the calcining unit as well as its adaptability to different calcination behavior, dependent on the properties of the meal, such as the agglomeration behavior of the preheated raw meal, are improved.
In accordance with the method employed for the thermal treatment of raw meal for the manufacture of cement, the preheated raw cement meal is divided into two substreams before calcination. These substreams are exposed to the exhaust air from the coolers and to the kiln exhaust gases. The substreams are conducted through the calcination zone parallel to one another. The subsequent joining and the parallel guidance of the two gas streams intermixed with the preheated raw meal occurs with the two substreams with meal being conducted through the calcinator at substantially identical gas velocity. Upon exiting from the calcinator, only a partial mixing occurs at the boundary layer of the two gas streams. This method is utilized because of its capability to largely prevent the inhibition effect of the evaporating alkalies on the burn-out of the fuels introduced at the calcination stage and this is intended to noticeably reduce the NO.sub.x portion in the kiln exhaust gas.
An object of the invention is to utilize the foregoing method, employing the advantageous results thereof and to provide a method and apparatus enabling the employment of fuels that are extremely difficult to burn for calcining the preheated raw meal in the manufacture of cement and utilizing an optimum exploitation of the thermal energy present in the fuel.
A further object of the invention is to provide an improved method and apparatus for the manufacture of cement from meal which has overall advantages in improved performance, quality, control and throughput utilizing fuels which are difficult to burn which may be otherwise termed as low grade fuels.